Air Cooled Exchangers Manifold & Bundle Arrangements

1. Purpose

This procedure describes the use of special inlet and outlet manifold and bundle arrangements for air cooled exchangers.

2. General

Normally, the contractor selects the manifold arrangement for all services with a single phase (either all vapor or all liquid) at the inlet. These contractor arrangements are noted on the Piping & Instrument Diagram (P&ID) as a Type “D” manifold.

3. Guidelines

The following guidelines address applications that require more stringent arrangements.

3.1 Two Phase Flow

Concern arises when the inlet stream to the exchanger is two phase mixture. The relative difference between the densities of the two phases may cause the liquid or vapor phase to flow preferentially through the tube bundles. This, in turn, may cause all liquid to go through some bundles and all vapor to go through other bundles, causing a reduction in overall exchanger performance. Such maldistribution can occur when the inlet piping is parallel to the tube bundle headers with no allowance for splitting the flow to the bundles equally (reference Attachment 1, Figure 1). Although such a manifold arrangement is acceptable for single phase services, it is not recommended for two phase flow.

3.2 Type “C” Manifold

Specifying a Type “C” manifold arrangement is one way to improve the distribution of vapor and liquid to each bundle (reference Attachment 1, Figure 2). In this arrangement, the piping allows the inlet stream to split to each bundle almost equally. This arrangement uses additional elbows in the piping, which increases the cost of the piping and adds pressure drop to the circuit. Since the outlet manifold is not symmetrical around each pair of bundles, some minor maldistribution between bundles may occur. Specify Type “C” manifolds when two phase flow occurs and pressure drop is not a problem.

3.3 Type “E” Manifold

Specify a Type “E” manifold when additional pressure drop is undesirable or the pressure drop must be minimized, e.g., in product condensers for Platforming, Pacol, Isomar, and Tatoray units (reference Attachment 2, Figure 1). In this arrangement, the piping is symmetrical only around the entire exchanger inlet and outlet, not around each pair of bundles. This arrangement, compared to a manifold with no special arrangement, results in a lower pressure drop and better flow distribution.

3.4 Type “F” Manifold

A special concern exists for some hydroprocessing units where the two phase reactor effluent is washed with water to prevent corrosion and plugging by salts. Type F manifolds should be considered for Naphtha Hydrotreating applications where significant quantities of sulfur and nitrogen exist in the feedstock. For example, units with coker naphtha could require this configuration. For these applications, specify a Type “F” manifold with completely symmetrical inlet and outlet piping (reference Attachment 2, Figure 2). This arrangement virtually ensures an equal distribution of vapor and liquid, including the water phase, to each bundle.

3.5 Type “Y” Manifold

The Type “Y” manifold is essentially the same as the Type “F” manifold except that it indicates multiple bundles within a single bay. Reference Attachment 2, Figure 3.

3.6 Project Specifications and P&ID

When specifying the manifold for a particular exchanger, indicate the type of manifold to use, i.e., “C,” “E,” “F,”, “Y” or “D” (by contractor), on the P&ID, in parenthesis, under the item number of the exchanger. A sketch of the “C,” “E,” and “F” manifolds, with appropriate notes, shall appear on the P&ID General Details and Notes drawing. In addition, bundle requirements are indicated by special notes that appear on the 402 Air Cooled Exchanger Project Specification sheet (reference Attachment 3).

4. Questions Regarding Arrangements

Direct any questions regarding the suitability of a particular manifold and bundle arrangement to the appropriate Technology, Process, or Equipment Specialist for resolution.

Attachment 1

Figure 1

Figure 2

Attachment 2

Figure 1

Figure 2

Attachment 2 (Continued)

Figure 3

Attachment 3